High strength corrosion resistant casting alloy



United States Patent 3,252,793 HIGH STRENGTH CORROSION RESTSTANT CASTING ALLOY Alfred H. Hesse, La Grange, Ill., assiguor to R. Lavin & Sons, Inc., a corporation of Illinois No Drawing. Filed Apr. 1, 1964, Ser. No. 356,647 9 Claims. (Cl. 75157.5)

This invention relates to'copper base alloys, and is directed particularly to the provision of cupriferous alloys having a high degree of resistance to corrosion in moist oxidizing environments and high mechanical strength in the as-cast condition, and to cast metallic articles made of such alloys. This application is a continuation-in-part of my prior application Serial No. 152,061, filed November 13, 1961, now abandoned.

The new alloy is composed essentially of modest proportions of iron, nickel, aluminum and zinc, and a major proportion of copper, and preferably in addition contains other elements, particularly silicon. It is eminently suited for making articles of shapes most advantageously made by casting, which require a high degree of resistance to corrosion and greater mechanical strength than is available in the lower cost high-copper alloys without subjecting the metal to heat treatment or to substantial mechanical working.

. A substantial demand has long existed for a copper base alloy having high resistance to corrosion in damp atmospheres and high mechanical strength in the as-cast condition. Despite the antiquity of copper base alloys and the extensive studies that have been made of them, available alloys all fall short of meeting this demand, except perhaps in the case of a fewalloys which are costly to produce or are unsuited to economical handling in commercial foundaries. Although copper base alloys are noted for their resistance to corrosion in ordinary atmospheric exposures, most suchalloys which possess high tensile strengths (upwards of 55,000 psi) and good yield strengths (25,000 p.s.i. or higher), together with substantial ductility (indicated by an elongation upwards of 12% in two inches) are not adequately resistant to corrosion for uses in which they are exposed to aqueous environments. The most common of such alloys, such as the manganese bronzes and the aluminum bronzes, con-- tain substantial amounts of zinc or aluminum, and in damp environments are subjected to the types of corrosion known respectively as dezincification and dealuminification. Alloys such as the silicon bronzes and nickeltin bronzes which are highly resistant to corrosion in aqueous media do not possess high mechanical strength in the as-cast condition, but must be subjected either to substantial cold working or to heat treatment in order to raise their physical properties to fairly high valves. Such operations add to the expense of the alloy and to parts fabricated from it. Alloys such as the cupronickels, which possess both high mechanical strength and high resistance to corrosion, are relatively costly.

The present invention provides a copper base alloy containing nickel, aluminum, zinc and iron, and advantageously other elements also (particularly silicon), which is characterized by having a high tensile strength, a fairly high yield strength, and high ductility in the as-cast condition. It is highly resistant to all types of corrosion, including dezincification and dealuminification, to which other copper base alloys are subject in aqueous media or in moist oxidizing atmospheres. These advantages are achieved with compositions which are economically competitive with manganese bronzes and other relative low cost copper base alloys.

The new alloy is composed essentially of 1% to 5.5 iron, 1% to 5.5% nickel, 1.1% to 2.5% aluminum, 1%

3,252,793 Patented May 24, 1966 "Ice to 7% zinc and the balance copper except for the advantageous introduction of certain other elements. These other elements include particularly silicon in an amount up to 1.5%, although when high ductility is required (20% or more elongation in 2 inches) the silicon content should be no higher than 0.9%. The alloy may also contain up to 1% tin, up to 0.75% manganese, up to 1.5% lead, and up to 2% of impurities and minor alloying elements which do not essentially alter the character of the alloy (all percentages herein are by weight of the alloy).

Preferably alloys in accordance with the invention having high ductility and high strength in the as-cast condition are composed essentially of 1% to 5.5% iron, 2% to 5.5% nickel, 1.5 to,2.0% aluminum, 1% to 7% zinc, 0.5% to 0.9% silicon, up to 0.7% tin, up to 0. 6% manganese, up to 1% lead, up to 1% of impurities and minor alloying elements which do not essentially alter thecharacter of the 'alloy, and the balance copper. The copper content of the alloy generally is upwards of and in most cases exceeds The concentration each of iron and nickel in the new alloy, in the range from 1% to 5.5%, is not especially critical, although advantageously the nickel content exceeds 2% in order to develop high tensile and yield strengths. A nickel content in the upper portion of the stated range (from 4.0% to 5.5 is best used when tensile strengths substantially above 60,000 pounds per square inch in the as-cast condition are sought. However, :alloys having tensile strengths near or even exceeding 60,000 pounds per square inch can be produced with nickel contents in the lower portion of the stated range (say from 2% to 3%).

The aluminum content of the alloy is quite critical. At least about 1.1% should be present in order to assure substantial ductility in the as-cast condition. An aluminum content about 1.5 is particularly advantageous, because at such aluminum concentration the tensile and yield strengths as well as ductility of the alloy are high. Upwards of 2.5% aluminum should be avoided, for at such high aluminum concentrations the alloy becomes subject to dealuminification, with substantial loss of mechanical strength, in corrosive aqueous media. To assure maximum corrosion resistance, the aluminum content preferably does not exceed 2.0%. Thus in general, alloys having maximum ductility in combination with high mechanical strength and maximum resistance to corrosion including freedom from all risk of dealuminification are produced when the aluminum content is in the range from 1.5% to 2.0%.

Zinc is employed in the new alloy in a concentration from 1% to 7%, and generally advantageously in an amount from 3.5% to 70%. Zinc increases the hardness of the alloy and contributes to its tensile strength without significant loss in ductility. It is also a desirable ingredient from the standpoint of the casting properties of the alloy, as it increases fluidity and thus enhances castability' of the molten alloy. Also its use reduces the cost of the alloy. These advantages are not obtained to any significant extent if the zinc content is below about 1%. However, zinc should not constitute more than 7% by weight of the alloy, for at zinc concentrations higher than 7% the alloy becomes susceptible to dezincification in a corrosive aqueous media with consequent loss of mechanical strength.

Silicon is an advantageous component of the alloy. The silicon content may be as high as 1.5 when high as-cast yield strength is desired and only moderate ductility is required; and it may be omitted altogether. Prefe erably, however, it is used in an amount from 0.5% to 049% by weight. When used in the preferred amount, silicon contributes substantially to the tensile and yield strengths of the metal in the as-cast condition without significant impairment of the ductility of the alloy and without hardening it undesirably. The silicon content should not exceed 1.5%, for at higher concentrations it adversely affects ductility of the alloy as evidenced by substantially reduced elongations (only about 12% or so in two inches in alloys containing near 1.5% silicon, and above 22% in two inches in preferred alloys containing less than 0.9% silicon).

Manganese, in amounts up to 0.75%, is a desirable ingredient because it contributes to high yield strength, and hardens the alloy somewhat, without any adverse effect on tensile strength or ductility. Manganese also improves the castability of the alloy, particularly when zinc is absent or present only in a very low concentration.

The addition of a small percentage of tin, up to 1%, is desirable because of its contribution to high tensile and yield strengths and because it hardens the alloy somewhat without impairing its ductility. The presence of tin also adds to the corrosion resistance of the alloy.

Lead may be included in the alloy, in amounts up to rosion resistant characteristics of the new alloy. Also the ductility of the new alloy in the as-cast condition, as indicated by its high elongation, is one of its outstanding characteristics.

The foregoing values for physical properties are in general minimum properties for alloys made in accordance with the invention. It is easily possible to produce preferred alloys having in the as-cast condition an elongation of at least 25% in two inches, a tensile strength exceeding 60,000 p.s.i., and a yield strength exceeding 30,000 p.s.i. The Brinell hardness of the preferred alloy generally is in the range from 90 to 125, though it may be higher. These physical properties equal or even exceed those of many corrosion-resistant wrought copper base alloys, and thus make the alloy of the invention eminently suited for producing, by conventional foundry casting techniques, articles of irregular or complex shapes which in service must possess the combination of high resistance to corrosion and high mechanical strength.

Fe, percent" Ni, percent" Al, percent... Zn, percent..

Si, percent Sn, percent Elongation in 2 in., percent 0.." Brinell hardness (500 kg.)

Particular examples of alloys accordlng to the 1nvent1on are set forth 1n the followmg table:

Alloy A l Alloy B Alloy C Alloy D Alloy E I Alloy F 1 Alloy G 1.5 without marked impairment of mechanical properties or corrosion resistance, and with substantial improvement in the machinability of the alloy. The tolerance of the alloy to the presence of lead is particularly advantageous in commercial casting operations, because it is extremely diflicult in ordinary non-ferrous foundry operations to avoid lead contamination of alloys being melted and cast. While a lead content up to 1.5% is permissible, it is preferable to hold the lead content to below 0.3% when extensive machining of the alloy is not required, and to hold it to below 1% when good machinability is required.

Minor amounts of other elements may also be present in the alloy, with or without some contribution to its desirable properties. A small amount of phosphorous (up to 0.01%) either as a residual deoxidizer or as a minor alloying element, is not harmful, and useful alloys containing even more phosphorous can be prepared. Small amounts of antimony and magnesium also may be present without impairing the mechanical and other properties of the alloy. A small amount of sulfur also may be present in the alloy without significantly affecting its properties. Small amounts of other elements also may be present, either as impurities or as purposeful additions. In general up to a total of 2%, of these and other elements, which may become introduced into the metal as minor alloying constituents or as impurities in normal foundry casting operations, may be present without harmful effeet; but preferably the concentration of such elements does not exceed a total of 1%. The tolerance of the new alloy to such ingredients is one of its advantages which makes it particularly suited for economic casting in commercial non-ferrous foundries.

Alloys according to the invention when properly prepared possess tensile strengths of at least 55,000 p.s.i. and yield strengths of at least 20,000 p.s.i., with elongations of at least 12% and generally above 22% in two inches. Thus the mechanical strength of the alloy in the as-cast condition is high for a non-ferrous composition; and it is remarkably so for an alloy having the outstanding cor- Valve stems for large water main valves are among the articles which may with particular advantage be made of the new alloy. A typical valve stem for a six inch valve, for example, is eighteen inches long and throughout most of its length is about 1% inches in diameter, but is formed with a collar about 2 /2 inches in diameter near its mid point. On one side of the collar the stem is threaded, and on the other side it is smooth-turned. Blanks for such valve stems are readily formed of the new alloy by conventional foundry casting operations. As indicated above, it is a major advantage of the new alloy that in the as-cast condition it possesses high mechanical strength (both high tensile strength and good yield strength), together with adequate ductility and hardness, so that no mechanical working or heat treatment is required to prepare the alloy for valve stem use. All that is necessary is to machine the casting to finished dimensions to produce a valve stem that meets the most rigid strength and corrosion resistance specifications.

The new alloy is easily melted and cast in commercial non-ferrous foundries. Melting and casting techniques are for the most part conventional. For example, the alloy may be prepared by melting the copper, or an alloy of copper with one or more of the other ingredients in any desired proportions, and adding the remaining ingredients in either commercially pure form or in the form of master alloys, either before or after the copper has been melted, to produce a melt of the desired composition. Use may also be made of various appropriate types of alloy scrap, such as aluminum bronze, silicon bronze, yellow brass, tin bronze, and the like, in making up a melt of the new alloy. The melt may be formed at temperatures in the range from 2,000 to 2,400 F.; and advantageously is cast at about 1,950 F. Conventional said molds, with conventional gating and risering, may be employed to form the castings.

It is very desirable to purge the alloy melt prior to casting with a non-oxidizing gas Preferably dry nitrogen is passed through the melt for about ten minutes shortly prior to pouring. Such treatment of the melt has been found to result in castings having notably greater tensile strength and ductility than corresponding castings made from melts not treated with nitrogen or other purging gas. As an example, an alloy according to the invention was melted and heated to 2,400 F. under normal oxidizing conditions, cooled to a pouring temperature of 1,950" to 1,980 F., and cast in a sand mold. The same alloy was also melted under similar oxidizing conditions, but treated by passing dry nitrogen through it for ten minutes as it cooled from 2,400 F. to pouring temperatures between 1,950 to 1,980 F. The following tabulation shows the notable increase in tensile strength and ductility Which the nitrogen treatment brought about:

1. A corrosion-resistant alloy having high ductility and high strength in the as-cast condition composed of 1% to 5.5 iron, 1% to 5.5 nickel, 1.1% to 2.5% aluminum, 1% to 7% zinc, up to 1.5% silicon, up to 1% tin, up to 0.75% manganese, up to 1.5% lead, up to 2% of impurities and minor alloying elements which do not essentially alter the character of the alloy, all percentages being by weight of the alloy, and the balance copper.

2. An alloy according to claim 1 containing not more than 0.9% silicon. I

3. An alloy according to claim 2 containing 0.5% to 0.9% silicon.

1. An alloy according to claim 1 containing 1.5 to 2% aluminum.

5. An alloy according to claim 1 containing less than 0.3% lead.

6. A corrosion-resistant alloy having high ductility and high strength in the as-cast condition composed of 1% to 5.5% iron, 2% to 5.5% nickel, 1.5% to 2.0% aluminum, 1% to 7% zinc, 0.5% to 0.9% silicon, up to 0.7% tin,

up to 0.6% manganese, up to 1% lead, up to 1% of impurities and minor alloying elements which do not essentially alter the character of the alloy, all percentages being by Weight of the alloy, and the balance copper.

7. An alloy according to claim 6 containing 3.5% to 7% zince.

8. A cast corrosion-resistant metallic article composed of an alloy of 1% to 5.5% iron, 1% to 5.5% nickel, 1.1% to 2.5% aluminum, 1% to 7% zinc, up to 1.5% silicon, up to 1% tin, up to 0.75% manganese, up to 1.5% lead, up to 2% impurities and minor alloying elements which do not essentially alter the character of the alloy, all percentages being by weight of the alloy, and the balance copper, said article being characterized by having in the as-cast condition an elongation of at least 12% in 2 inches, a tensile strength of at least 55,000 p.s.i. and a yield strength of at least 20,000 p.s.i.

9. A cast corrosion-resistant metallic article composed of an alloy of 1% to 5.5% iron, 2% to 5.5% nickel, 1.5% to 2.0% aluminum, 1% to 7% zinc, 0.5% to 0.9% silicon, up to 0.7% tin, up to 0.6% manganese, up to 1% lead, up to 1% of impurities and minor alloying elements which do not essentially alter the character of the alloy, all percentages being by weight of the alloy, and the balance copper, said article being characterized by having in the as-cast condition an elongation of at least 25% in 2 inches, a tensile strength exceeding 60,000 p.s.i., and a yield strength exceeding 30,000 p.s.i.

References (Iited by the Examiner UNITED STATES PATENTS 1,481,782 1/1924 Iytaka -159 1,815,071 7/ 1931 Price 75-1575 2,031,316 2/1936 Jennison 75-162X 2,101,087 12/1937 Munson 75157.5 2,188,681 1/1940 Freeman et al 75157.5 2,400,234 5/1946 Hudson 75157.5 X 2,430,419 11/1947 Edens 75-162 2,789,900 4/1957 Hannon 75-159 2,810,641 10/1957 Roberts 75-159 DAVID L. RECK, Primary Examiner. 

1. A CORROSION- RESISTANT ALLOY HAVING HIGH DUCTILITY AND HIGH STRENGTH IN THE AS-CAST CONDITION COMPOSED OF 1% TO 5.5% IRON, 1% TO 5.5% NICKEL, 1.1% TO 2.5% ALUMINUM, 1% TO 7% ZINC, UP TO 1.5% SILICON, UP TO 1% TIN, UP TO 0.75% MANGANESE, UP TO 1.5% LEAD, UP TO 2% OF IMPURITIES AND MINOR ALLOYING ELEMENTS WHICH DO NOT ESSENTIALLY ALTER THE CHARACTER OF THE ALLOY, ALL PERCENTAGES BEING BY WEIGHT OF THE ALLOY, AND THE BALANCE COPPER. 